Shredding apparatus of various types are generally known in the art of materials processing, and are useful in numerous applications. These types of apparatus include, among others, hammermills. As generally understood in the art, hamermills include a rotor assembly rotatable about an axis which is generally horizontally disposed. The rotor assembly is typically driven by either electric motors or from internal combustion engines. Hammers are affixed to the rotor so as to describe a circle when the rotor is revolving. A grate, which is co-axial with the rotor axis, is typically semi-circular in shape and generally disposed in the lower half of the hammer circle. The grate is spaced away from the hammer circle so as to provide clearance from the moving hammers while also applying a cutting or shredding action to material coming between the hammers and the grate. Material to be shredded or reduced is typically delivered to the shredding apparatus by gravity feed or by mechanical means such as a conveyor belt, or air-driven or other force-feeding means. The material is thereby shredded, being broken up or reduced in size and exits the apparatus through openings in the grate.
Hammermills as described above are readily manufactured in a wide range of sizes and capacities, and are especially suitable for high capacity applications where it is desired to reduce large volumes or masses of material in a short space of time. For example, the hammermill may be adapted to reduce heavy or high-mass-to-volume materials such as automobile tires, or to relatively light, low-mass-to-volume materials such as aluminum scrap or residential refuse. However, difficulties have arisen in the application of hammermill apparatus.
When reducing heavy or tough materials such as automobile tires, the hammermill typically suffers a high degree of wear to both the hammers and the grate. In these applications, the hammermill components are often subject to a high degree of shock, since the materials being reduced are relatively high-strength and durable. For example, automobile tires often contain nylon, polyester or steel belts throughout the body of the tire, and these materials, as well as the rubber from which the tire body is formed, are designed to be strong and resistant to either breakage or cutting. Typically, the hammermill components are formed of steel and may be hardened or provided with a case-hardened surface to improve the strength and wear resistance of the components.
Another phenomenon known generally as windage affects the operation of the hammermill apparatus primarily in the reduction of relatively lighter materials. Windage refers to the flow of air generated by the relatively high-speed rotation of the rotor. Generally, this airflow tends to undesirably slow the flow of the material into the hammermill, and may cause a backup of infed material at the hammermill inlet. Furthermore, windage may cause a circular flow of material within the hammermill itself, which can substantially reduce the capacity of the apparatus. Either flow condition can cause the apparatus to function in an undesirable manner, causing the infed material to enter the apparatus in slugs, resulting in uneven operation or even plugging and stopping of the rotor in some instances. Such flow conditions as these can cause substantial damage to the hammermill apparatus, but in any event reduce the effective capacity of the apparatus.
The flow of material within the typical hammermill apparatus is also affected during the ongoing operation of the apparatus by the undesirable accumulation of material within and between the components of the apparatus. In practice, it is typical for a portion of the material to become compacted between the hammers of the rotor assembly, interfering with the flow of material within the hammermill apparatus. Obviously, this packed material also reduces the available material flow area within the hammermill apparatus, sometimes to the extent that the apparatus is virtually unable to process the materials. This problem is exacerbated with material which is lightweight and relatively easily crushed or compacted, an example of which is the aluminum can in common use for containing consumer goods such as cola or soda, since this material is also more subject to the effects of windage. Other materials which present similar difficulties are such thin, flexible materials as paper, corrugated stock, wood veneers and sheet metals. Such material tends to be readily formed, and under the impact of the hammer element, will be formed onto the hammer element. The material can then build up in layers on the hammers and become compacted between the hammers of the rotor assembly, interfering with the flow of material within the hammermill apparatus. Obviously, this packed material also reduces the available material flow area within the hammermill apparatus, sometimes to the extent that the apparatus is virtually unable to process the materials.
In the typical rotor assembly, the rotor includes a rotor provided with a number of hammer elements affixed thereto. As the apparatus is operated for extended periods, portions of the materials reduced in the hammermill tend to accumulate between the hammer elements. This accumulation, as it increases, concurrently reduces the material flow capacity of the apparatus. At some point, the apparatus must be stopped and the accumulation must be manually removed from the rotor assembly before operation can be successfully resumed.
The effects of the windage in causing slugs of the infed material to enter the apparatus, in combination with the compaction effect of the materials within the rotor assembly and, in some cases, in the grate assembly as well, can necessitate fairly frequent shutdowns of the apparatus for cleaning and removal of the accumulated material. Such cleanings are arduous and time-consuming and therefore relatively expensive in terms of labor costs alone, and substantial costs may be incurred due to loss of business and other downtime costs as well.
Therefore, it is an object of the present invention to provide a hammermill apparatus as will operate to efficiently reduce readily compacted or compressed materials.
It is another object of the present invention to provide a hammermill apparatus such as will reduce such materials while incurring little or no accumulation of the materials in the hammermill apparatus.
It is yet a further object of the present invention to provide such a hammermill apparatus as will be relatively inexpensive to repair and maintain.
It is another object of the present invention to provide such a hammermill apparatus as will be relatively simple and cost-effective to manufacture.
These and other objectives of the present invention will become apparent in the specification and claims that follow.